The present invention relates to an optical information medium having an organic information layer. More specifically, the present invention relates to an optical information medium with an overcoat layer coated over the organic information layer.
The use of overcoat layers is well known in the optical information media art. Such layers are employed for many different purposes, e.g., as a thermal or mechanical barrier.
For example, in U.S. Pat. No. 4,069,487, there is disclosed a recording member for recording a laser beam bearing information by the deformation of a recording layer. The recording member is comprised of a support, the recording layer and an overcoat protecting layer which is not destroyed by the laser beam. The overcoat protecting layer can be an organic material or an inorganic material. Among the organic materials mentioned are organic high polymers such as nitrocellulose resins, polyvinyl chloride resins, polycarbonate resins and acrylic resins. The thickness of the protecting layer is generally in the range of from 0.1 to 10 microns.
In U.S. Pat. No. 4,584,259 there is disclosed an optical recording medium having an acrylic overcoat. The overcoating structure employed is somewhat complex, as it comprises a "soft pad" layer on the absorber, with a "hard" layer (e.g., a radiation cured acrylic) laid over the soft pad as an outer protective overcoat.
U.S. Pat. No. 4,340,655 discloses optical recording elements having a thermal and mechanical barrier layer coated over the recording layer. The thermal and mechanical barrier layer comprises water soluble polymers having a glass transition temperature when dry of at least 100.degree. C., and preferably at least 150.degree. C. The barrier layer coated over the information layer is generally of a thickness on the order of 1,500 angstroms or more. Such a thickness is believed needed to avoid rupturing during the recording process. See also, U.S. Pat. No. 4,101,907 which discloses an optical recording medium comprised of a light absorbing material which is coated with a transparent barrier layer and overcoated with a relatively thick transparent protective layer.
U.S. Pat. No. 4,527,173 discloses an erasable, reusable optical recording element having a heat-deformable recording layer overcoated with a transparent layer. The transparent overcoat has a thickness of between 0.05 microns up to 0.1 microns. The transparent overcoat is preferably made from a ceramic material, including aluminum oxide, silicon monooxide, silicon dioxide glass, silica, quartz and magnesium fluoride.
U.S. Pat. No. 4,636,804 pertains to a recording medium comprising a microporous polymer recording layer which is coated with a polymeric coating. The polymeric molecules of the coating are of sufficient molecular size or branching to preclude entry of the polymer molecules into the pores of the microporous polymer recording layer. Due to the polymeric coating employed over the microporous polymer recording layer, the recording medium exhibits an enhanced signal to noise ratio upon the reading of the recorded information.
The search for more effective and useful optical media is continuously ongoing. Any discoveries relating to improvements in the sensitivity, marking ability and noise reduction of optical media would be of a great benefit to the art.
Accordingly, it is an objective of the present invention to provide a novel, effective and useful optical information medium containing an organic information layer.
It is another object of the present invention to provide such an optical information medium which exhibits a sharper threshold in the marking of information in the recording layer.
Yet another object of the present invention is to provide such an optical information medium which exhibits improved carrier to noise ratio.
It is still another object of the present invention to provide a novel information medium having a specific overcoat layer coated over an organic information layer.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.